U.S. patent application number 11/474484 was filed with the patent office on 2007-05-17 for wafer redistribution structure with metallic pillar and method for fabricating the same.
This patent application is currently assigned to Advanced Semiconductor Engineering, Inc.. Invention is credited to Jian-Wen Lo.
Application Number | 20070111499 11/474484 |
Document ID | / |
Family ID | 38041475 |
Filed Date | 2007-05-17 |
United States Patent
Application |
20070111499 |
Kind Code |
A1 |
Lo; Jian-Wen |
May 17, 2007 |
Wafer redistribution structure with metallic pillar and method for
fabricating the same
Abstract
A wafer structure and a method for fabricating the same are
provided. The wafer structure comprises a substrate, a
redistribution structure, a passivation layer, an under bump
metallurgy (UBM) layer and a bump. The substrate has a solder pad.
The redistribution structure is formed on the substrate and
comprises a copper pillar electrically connected to the solder pad.
The passivation layer is formed on the redistribution structure and
has an aperture to expose the copper pillar. The UBM layer is
formed in the aperture and disposed on the copper pillar. The bump
is formed on the UBM layer.
Inventors: |
Lo; Jian-Wen; (Banciao City,
TW) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
Advanced Semiconductor Engineering,
Inc.
|
Family ID: |
38041475 |
Appl. No.: |
11/474484 |
Filed: |
June 26, 2006 |
Current U.S.
Class: |
438/612 ;
257/734; 257/E21.508; 257/E23.02; 257/E23.021 |
Current CPC
Class: |
H01L 2924/01078
20130101; H01L 2924/14 20130101; H01L 24/06 20130101; H01L
2224/1147 20130101; H01L 2924/01029 20130101; H01L 2924/01013
20130101; H01L 24/11 20130101; H01L 2924/01023 20130101; H01L
2924/01028 20130101; H01L 2924/01006 20130101; H01L 2224/023
20130101; H01L 24/13 20130101; H01L 2924/01042 20130101; H01L 24/05
20130101; H01L 2924/01074 20130101; H01L 2224/131 20130101; H01L
2924/01005 20130101; H01L 2924/01024 20130101; H01L 24/03 20130101;
H01L 2224/05001 20130101; H01L 2224/05555 20130101; H01L 2224/0554
20130101; H01L 2924/01022 20130101; H01L 2924/014 20130101; H01L
2224/0401 20130101; H01L 2224/13099 20130101; H01L 2224/131
20130101; H01L 2924/014 20130101; H01L 2924/00014 20130101; H01L
2224/05555 20130101; H01L 2924/00014 20130101; H01L 2224/023
20130101; H01L 2924/0001 20130101 |
Class at
Publication: |
438/612 ;
257/734 |
International
Class: |
H01L 21/44 20060101
H01L021/44; H01L 23/48 20060101 H01L023/48 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 15, 2005 |
TW |
94140168 |
Claims
1. A wafer structure, comprising: a substrate having a solder pad
and a first passivation layer, wherein the first passivation layer
has a first aperture to expose the solder pad; a redistribution
structure formed on the substrate, comprising: at least one
redistribution layer electrically connected to the solder pad,
wherein the redistribution layer has at least one top portion and
an indented portion; a metallic pillar for filling the indented
portion, wherein the metallic pillar is protruded from the top
portion; and a second passivation layer formed on the first
passivation layer, wherein the second passivation layer surrounds
the metallic pillar; a third passivation layer formed on the
redistribution structure, wherein the third passivation layer has a
third aperture to expose the metallic pillar; an under bump
metallurgy (UBM) layer formed in the third aperture and disposed on
the metallic pillar with respect to the indented portion; and a
bump formed on the UBM layer.
2. The wafer structure according to claim 1, wherein the metallic
pillar is a copper pillar.
3. The wafer structure according to claim 1, wherein the top
surface of the second passivation layer is disposed at the same
height with the top surface of the metallic pillar.
4. The wafer structure according to claim 1, wherein the
redistribution layer is formed in the first aperture and on the
first passivation layer, the top portion covers the first
passivation layer, and the indented portion is disposed in the
first aperture.
5. A wafer structure, comprising: a substrate having a solder pad;
a redistribution structure formed on the substrate, wherein the
redistribution structure comprises at least one copper pillar
electrically connected to the solder pad; a passivation layer
formed on the redistribution structure, wherein the passivation
layer has an aperture to expose the copper pillar; an under bump
metallurgy (UBM) layer formed in the aperture and disposed on the
copper pillar; and a bump formed on the UBM layer.
6. The wafer structure according to claim 5, wherein the
redistribution structure further comprises: at least one
redistribution layer electrically connected to the solder pad,
wherein the redistribution structure has at least one top portion
and an indented portion; wherein the copper pillar fills the
indented portion and is protruded from the top portion.
7. The wafer structure according to claim 6, further comprising a
first passivation layer having a first aperture to expose the
solder pad; wherein the redistribution layer is formed in the first
aperture and on the first passivation layer, and the top portion
covers the first passivation layer, and the indented portion is
disposed in the first aperture.
8. The wafer structure according to claim 7, further comprising a
second passivation layer formed on the first passivation layer,
wherein the second passivation layer surrounds the copper pillar,
and the top surface of the second passivation layer is disposed at
the same height with the top surface of the copper pillar.
9. A method for fabricating a wafer structure, comprising:
providing a substrate having a solder pad and a first passivation
layer, wherein the first passivation layer has a first aperture to
expose the solder pad; forming a redistribution layer on the first
passivation layer and in the first aperture, wherein the
redistribution structure has an indented portion; forming a
metallic pillar to fill the indented portion, wherein the metallic
pillar is protruded from the redistribution layer; forming a second
passivation layer on the first passivation layer, wherein the
second passivation layer surrounds the metallic pillar; forming a
third passivation layer on the second passivation layer, wherein
the third passivation layer has a third aperture to expose the
metallic pillar; forming an under bump metallurgy (UBM) layer in
the third aperture and on part of the third passivation layer,
wherein the UBM layer is electrically connected to the metallic
pillar with respect to the indented portion; and forming a bump on
the UBM layer.
10. The method according to claim 9, wherein the step of forming
the redistribution layer on the substrate comprises: forming a
metallic layer on the first passivation layer and in the first
aperture; and patterning the metallic layer to form the
redistribution layer; wherein the redistribution layer is disposed
in the first aperture to form the indented portion and covers the
first passivation layer to form a top portion.
11. The method according to claim 9, wherein the step of forming
the metallic pillar comprises: forming a photo-resist layer on the
first passivation layer and the redistribution layer; patterning
the photo-resist layer to form a slot to expose the indented
portion; and forming the metallic pillar in the slot by
electroplating, wherein the metallic pillar fills the indented
portion and is protruded from the redistribution layer.
12. The method according to claim 9, wherein the redistribution
layer is formed by etching the metallic pillar.
13. The method according to claim 9, wherein the metallic pillar is
a copper pillar.
14. The method according to claim 9, wherein the top surface of the
second passivation layer is disposed at the same height with the
top surface of the metallic pillar.
15. The method according to claim 9, wherein the first passivation
layer, the second passivation layer and the third passivation layer
include polyimide (Pl).
16. The method according to claim 9, wherein the step of forming
the redistribution layer and the step of forming the metallic
pillar comprise: forming a metallic layer on the first passivation
layer and in the first aperture, wherein the metallic layer
disposed in the first aperture forms the indented portion; forming
a photo-resist layer on the metallic layer; patterning the
photo-resist layer to form a slot to expose the indented portion;
and forming the metallic pillar in the slot by electroplating,
wherein the metallic pillar fills the indented portion and is
protruded from the metallic layer; removing the photo-resist layer;
and patterning the metallic layer according to the metallic pillar
to form the redistribution layer; wherein the redistribution layer
disposed in the first aperture forms the indented portion and
covers the first passivation layer to form a top portion.
Description
[0001] This application claims the benefit of Taiwan application
Ser. No. 94140168, filed Nov. 15, 2005, the subject matter of which
is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates in general to a wafer structure and a
method for fabricating the same, and more particularly to a
redistribution structure of a wafer structure and a method for
fabricating the same.
[0004] 2. Description of the Related Art
[0005] In response to the requirements with regards to the
integration and miniaturization of electronic devices, the
packaging technology of integrated circuits (ICs) is headed towards
miniaturization and high density. Examples of the packaging
technology of high-density integrated circuits including the ball
grid array (BGA) technology, the chip-scale package (CSP)
technology, the flip chip (F/C) technology, and the multi-chip
module (MCM) technology are provided. In terms of a high-density
integrated circuit, that is, an integrated circuit having more pins
per unit area, the speed of signal transmission will be improved if
the length of wiring distribution is shortened. Therefore, the
application of the metallic pillar capable of shortening the length
of wiring distribution has gradually replaced the application of
routing and become a mainstream practice in high-density packaging
technology.
[0006] The solder pads disposed on the chip being so close to each
other that the bumps disposed on the solder pads are likely to be
electrically connected to each other, causing the occurrences of
unexpected short-circuits. Besides, the solder pads being so close
to the sawing line of the wafer that the bumps are likely to be
sawn when the wafer is being sawn. Therefore, the current bumping
technology changes the disposition of the bumps by redistribution.
Under certain circumstances, the redistribution layer has to be
crisscrossed with the layout path due to the overall layout of the
chip, and the three-layered redistribution structure is thus
invented.
[0007] However, in the three-layered redistribution structure, some
of the contacts directly form bumps above the original position of
the solder pads, making the bumps to be positioned too low.
Referring to FIG. 1, a cross-sectional view according to a
conventional wafer structure having a three-layered redistribution
structure is shown. The conventional wafer structure 10 includes a
substrate 11, two solder pads 12 and 14, a first passivation layer
20, two first redistribution layers 22 and 24, a second passivation
layer 30, two second redistribution layers 32 and 34, a third
passivation layer 40, an under bump metallurgy (UBM) layer 42, two
bumps 52 and 54. The substrate 11 has several solder pads 12, 14
and the first passivation layer 20 disposed thereon. The first
passivation layer 20 has several first apertures to expose the
solder pads 12 and 14.
[0008] The solder pads 12 and 14 respectively adopt different
designs of redistribution layers. The solder pad 14 is extended to
the right via the first redistribution layer 24 and the second
redistribution layer 34, and forms an under bump metallurgy (UBM)
layer 44 and a bump 54 at one end of the second redistribution
layer 34. A component is electrically connected to the solder pad
14 by contacting the bump 54, thereby redistributing the electrical
contacts of the wafer 10. On the other hand, the bump 52
electrically connected to the solder pad 12 is predetermined to be
formed above the original position of the solder pad 12. Similarly,
the solder pad 12 is extended upwardly via the first redistribution
layer 22 and the second redistribution layer 32, and forms the UBM
layer 42 and the bump 52 in the second redistribution layer 32. It
is noted that an obvious height drop x1 exists between the bump 52
and the bump 54. That is to say, the design of adopting the
three-layered redistribution layer and forming the bump 52 on the
solder pad 14 would easily cause the bump 52 to be positioned too
low, severely affecting the subsequent packaging process.
[0009] Referring to FIG. 2, another cross-sectional view according
to the conventional wafer structure having the three-layered
redistribution layer is shown. The solder pad 16 is slightly
extended to the left via the first redistribution layer 26 and the
second redistribution layer 36, and forms an under bump metallurgy
(UBM) layer 46 and a bump 56 in the second redistribution layer 36.
The contact area between the first redistribution layer 26 and the
second redistribution layer 36 is too small, so the two layers are
likely to come off the structure, severely damaging the electrical
characteristics of the components.
[0010] Generally speaking, despite the conventional three-layered
redistribution layer resolves the problem of crisscrossed circuits,
however, when the bump is formed above the solder pad or the
extension distance is too short, the bumps are likely to come off
the structure if the bumps are positioned too low. The above two
problems severely restrict the application of the conventional
three-layered redistribution layer, and yet the problems of
crisscrossed circuits still remain unresolved.
SUMMARY OF THE INVENTION
[0011] It is therefore an object of the invention to provide a
redistribution structure of a wafer structure and a method of
fabricating the same. The design adopts a multi-layered
redistribution structure, avoiding the occurrences of
short-circuits when the circuits are crisscrossed. The bumps are of
the same height, thus avoiding height drop. Furthermore, the
redistribution layers of the redistribution structure have good
contacts and are not easy to be detached.
[0012] The invention achieves the above-identified object by
providing a wafer structure including a substrate, a redistribution
structure, a third passivation layer, an under bump metallurgy
(UBM) layer and a bump. The substrate has a solder pad and a first
passivation layer. The first passivation layer has a first aperture
to expose the solder pad. The redistribution structure is formed on
the substrate. The redistribution structure includes at least one
redistribution layer, a metallic pillar and a second passivation
layer. The redistribution layer is electrically connected to the
solder pad, and has at least one top portion and an indented
portion. The metallic pillar fills the indented portion and is
protruded from the top portion. The second passivation layer is
formed on the first passivation layer and surrounds the metallic
pillar. The third passivation layer is formed on the redistribution
structure and has a third aperture to expose the metallic pillar.
The UBM layer is formed in the third aperture and disposed on the
metallic pillar with respect to the indented portion. The bump is
formed on the UBM layer.
[0013] The invention further achieves the above-identified object
by providing a wafer structure. The wafer structure includes a
substrate, a redistribution structure, a passivation layer, an
under bump metallurgy (UBM) layer and a bump. The substrate has a
solder pad. The redistribution structure is formed on the
substrate. The redistribution structure includes at least one
copper pillar electrically connected to the solder pad. The
passivation layer is formed on the redistribution structure and has
an aperture to expose the copper pillar. The UBM layer is formed in
the aperture and is disposed on the copper pillar. The bump is
formed on the UBM layer.
[0014] The invention further achieves the above-identified object
by providing yet another method of fabricating a wafer structure.
The method includes the following steps. (a). Providing the
substrate having the solder pad and the first passivation layer,
wherein the first passivation layer has a first aperture to expose
the solder pad. (b). Forming a redistribution layer on the first
passivation layer and the first aperture, wherein the
redistribution layer has an indented portion. (c). Forming a
metallic pillar to fill the indented portion, wherein the metallic
pillar is protruded from the redistribution structure. (d). Forming
a second passivation layer on the first passivation layer, wherein
the second passivation layer surrounds the metallic pillar. (e).
Forming a third passivation layer on the second passivation layer,
wherein the third passivation layer has a third aperture to expose
the metallic pillar. (f). Forming an under bump metallurgy (UBM)
layer in the third aperture and on part of the third passivation
layer, wherein the UBM layer is electrically connected to the
metallic pillar with respect to the indented portion. (g). Forming
a bump on the UBM layer.
[0015] Other objects, features, and advantages of the invention
will become apparent from the following detailed description of the
preferred but non-limiting embodiments. The following description
is made with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 (Prior Art) is a cross-sectional view according to a
conventional wafer structure having a three-layered redistribution
structure;
[0017] FIG. 2 (Prior Art) is another cross-sectional view according
to the conventional wafer structure having the three-layered
redistribution structure;
[0018] FIG. 3 is a cross-sectional view of a wafer structure
according to a preferred embodiment of the invention;
[0019] FIGS. 4A.about.4J are flowcharts of a method of fabricating
a wafer structure according to the preferred embodiment of the
invention; and
[0020] FIG. 5 is a perspective of the redistribution structure of
the wafer structure according to FIG. 4J.
DETAILED DESCRIPTION OF THE INVENTION
[0021] The invention provides a multi-layered redistribution
structure and a method for fabricating the same, avoiding the
occurrences of short-circuits even when circuits are crisscrossed.
According to the invention, the bumps have the same height and are
without height drop. At the contact point of the redistribution
layer extended from the original position of the solder pad, a
metallic pillar is used to fill the indented portion and elevate
the under bump metallurgy (UBM) layer, so that the bump extended
from the original position of the solder pad has the same height
with the bump positioned elsewhere.
[0022] Referring to FIG. 3, a cross-sectional view of a wafer
structure according to a preferred embodiment of the invention is
shown. The wafer structure 100 of the present embodiment of the
invention includes a substrate 110, a redistribution structure 234,
a third passivation layer 170, an under bump metallurgy layer (UBM)
180 and a bump 190. The substrate 110 has a solder pad 112 and a
first passivation layer 118. The first passivation layer 118 has a
first aperture to expose the solder pad 112. The redistribution
structure 234 is formed on the substrate 110. The redistribution
structure 234 includes at least one redistribution layer 120, a
metallic pillar 130 and a second passivation layer 140. The
redistribution layer 120 electrically connected to the solder pad
112 has at least one top portion 120b and an indented portion 120a.
The metallic pillar 130 fills the indented portion 120a and is
protruded from the top portion 120b. The second passivation layer
140 is formed on the first passivation layer 118 and surrounds the
metallic pillar 130. The third passivation layer 170 formed on the
redistribution structure 234 has a third aperture 170a to expose
the metallic pillar 130. The UBM layer 180 formed in the third
aperture 170a is disposed on the metallic pillar 130 with respect
to the indented portion 120a. The bump 190 is formed on the UBM
layer 180.
[0023] In other words, the redistribution layer 120 is formed in
the first aperture and on the first passivation layer 118. The top
portion 120b covers the first passivation layer 118. The indented
portion 120a is disposed in the first aperture 118a. Preferably,
the metallic pillar 130 is a copper pillar possessing excellent
features of conductivity and hardness. The metallic pillar 130,
preferably ranging from 5 .mu.m to 8 .mu.m, fills the indented
portion 120a of the redistribution layer 120 and is protruded from
the top portion 120b of the redistribution layer 120. By doing so,
the top surface of the second passivation layer 170 is disposed at
the same height with the top surface of the metallic pillar 130,
therefore the UBM layer 180 disposed on the metallic pillar 130 is
approximately of the same height with the UBM layer 180 disposed on
the second passivation layer 170. That is to say, the top surface
of the redistribution structure formed above or near the original
position of the solder pad has the same height with the top surface
of the redistribution structure extended outwardly from the solder
pad. Therefore, the UBM layer and the bump formed under the same
conditions would have the same height.
[0024] Referring to FIGS. 4A.about.4J, several flowcharts of a
method of fabricating a wafer structure according to the preferred
embodiment of the invention are shown. Each flowchart includes an
upper view and a cross-sectional view viewed along the
cross-sectional line of the upper view. The steps of the method for
fabricating the wafer structure of the present embodiment of the
invention are disclosed below.
[0025] Firstly, as shown in FIG. 4A, a substrate 110 having several
solder pads 112, 114, and 116 and a first passivation layer 118 is
provided, wherein the first passivation layer 118 has a first
aperture 118a to expose the solder pads 112, 114, and 116.
Furthermore, for the bump of the solder pad 112 to be formed at the
original position, the redistribution layer of the solder pad 114
must crisscross with the redistribution layer of the solder pad
116. Therefore, the redistribution structures of the solder pads
112, 114, and 116 are different from one another.
[0026] Next, a redistribution layer and a metallic pillar are
formed. The preferable way of forming the metallic layer includes
the following steps. Referring to FIG. 4B, a metallic layer 122 is
formed on the first passivation layer 118 and the first aperture
118a. The metallic layer 122 disposed in the first aperture 118a
forms an indented portion 122a. The way of forming the metallic
layer 122 includes electroless plating, sputtering or chemical
deposition. Afterwards, a photo-resist layer 124 is formed on the
metallic layer 122. The photo-resist layer 124 is patterned to form
a slot 124a to expose the indented portion 122a. Examples of the
photo-resist layer 124 include a photo-resist solution or a dry
film. Then, the metallic pillar 130 formed in the slot 124a by
electroplating fills the indented portion 122a and is protruded
from the metallic layer 122. Preferably, the metallic pillar 130 is
a copper pillar. Next, the photo-resist layer 124 is removed as
shown in FIG. 4C. Afterwards, another patterned photo-resist layer
126 is formed on the metallic layer 122 as shown in FIG. 4D.
Lastly, the metallic layer 122 is patterned according to the
metallic pillar 130 and another patterned photo-resist layer 126 to
form several redistribution structures 120, 128 and 129 as shown in
FIG. 4E. Referring to FIG. 4E, the redistribution layer 120
disposed in the first aperture 118a forms an indented portion 120a
and covers the first passivation layer 118 forms a top portion
120b. To elaborate the above disclosure in greater details, the top
portion 120b of the redistribution layer 120 of the bump
predetermined to be formed at the original position is positioned
at the original position, while the top portion 129a of the
redistribution structure 129 of the bump predetermined to be formed
elsewhere extends a distance towards the predetermined position of
the bump on the first passivation layer 118. Particularly, the top
portion 128a of the redistribution structure 128 of the bump
predetermined to be formed elsewhere is also disposed at the
original position so as to crisscross with the redistribution
structure 129.
[0027] On the other hand, the redistribution layer and the metallic
pillar can be separately formed. For example, the redistribution
layer is first formed on the first passivation layer and the first
aperture to form the indented portion of the redistribution layer,
and then the metallic pillar is formed to fill the indented portion
and is protruded from the redistribution layer. The formation of
the redistribution layer includes the following steps: firstly, a
metallic layer is formed on the first passivation layer and the
first aperture; next, the metallic layer is patterned to form a
redistribution layer; the redistribution layer disposed in the
first aperture forms the indented portion and covers the first
passivation layer to form the top portion. Moreover, the formation
of the metallic pillar includes the following steps: a photo-resist
layer is formed on the first passivation layer and the
redistribution layer; the photo-resist layer is patterned to form a
first aperture to expose the indented portion; and a metallic
pillar is formed in the first aperture by electroplating, so that
the metallic pillar fills the indented portion and is protruded
from the redistribution layer.
[0028] Then, a second passivation layer 140 is formed on the first
passivation layer 118 and surrounds the metallic pillar 130 as
shown in FIG. 4F. The formation of the second passivation layer 140
includes rotary coating, chemical deposition, printing, draping,
spraying and other methods. Preferably, the top surface of the
second passivation layer 140 is disposed at the same height with
the top surface of the metallic pillar 130. Besides, several
apertures 140a are formed on the second passivation layer 140 to
expose the redistribution layers 128 and 129. Afterwards, the
second redistribution layers 132 and 134 are formed according to
the above method of formation as shown in FIG. 4G. Furthermore, the
top portion 132b of the redistribution layer 132 electrically
connected to the solder pad 114 extends a distance on the second
passivation layer 140, while the top portion 134b of the
redistribution layer 134 electrically connected to the solder pad
116 extends a distance towards another direction on the second
passivation layer 140 so as to crisscross with the redistribution
layer 132. Thus, the redistribution structure is completed.
[0029] Afterwards, a third passivation layer 170 is formed on the
second passivation layer 140. The third passivation layer 170 has a
third aperture 170a to expose the metallic pillar 130 as shown in
FIG. 4H. The way of forming the third passivation layer 170
includes rotary coating, chemical deposition, printing, draping,
spraying and other methods. Meanwhile, the third aperture 170a of
the third passivation layer also exposes the second redistribution
layers 132 and 134 of the redistribution structure. Preferably, all
of the first passivation layer, the second passivation layer and
the third passivation layer include polyimide (Pl).
[0030] Next, several UBM layers 180, 182, 184 are formed in the
third aperture 170a and on part of the third passivation layer 170
as shown in FIG. 41. The UBM layer is normally composed of an
adhesion layer, a diffusion barrier layer and a wetting layer. The
adhesion layer for providing adhesion between the solder pad and
the passivation layer includes aluminum, titanium, chromium,
tungsten-titanium alloy and other metals. The diffusion barrier
layer for preventing metal diffusion between the bump and the
solder pad includes nickel-vanadium alloy, nickel and other metals.
The wetting layer for providing draping between the under bump
metallurgy layer and the bump includes copper, molybdenum, platinum
and other metals. Besides, the UBM layer 180 is electrically
connected to the metallic pillar 130 with respect to the indented
portion 120a. Thus, the bottom of the UBM layer 180 formed on the
metallic pillar 130 is approximately disposed at the same height
with the bottom of the UBM layer 184 formed on the second
passivation layer 140. The cavity volume of the indented portion of
the UBM layer 180 formed on the metallic pillar 130 is
approximately the same with the cavity volume of the indented
portion of the UBM layer 184 formed on the second passivation layer
140.
[0031] Lastly, the slot formed by patterning the photo-resist is
filled with solder paste or electroplating solder and is disposed
on the UBM layers 180, 182 and 184, and then the bumps 190, 192,
and 194 are formed via the process of reflowing as shown in FIG.
4J; meanwhile, the patterned photo-resist is removed to complete
the wafer structure 100 of the present embodiment of the invention.
It is noted that the bumps 190, 192, and 194 are substantially of
the same height and are without vertical height drop. Since the
cavity volume of the indented portion of the UBM layer 180 is
approximately the same with the cavity volume of the indented
portion of the UBM layer 184, the amount of the solder paste or the
electroplating solder used the indented portion of the UBM layer
180 is approximately the same with amount of the solder paste or
the electroplating solder used to fill up the indented portion of
the UBM layer 184. Consequently, the bumps formed according to the
process of reflowing substantially have the same size and the same
height. Referring to FIG. 5, a perspective of the redistribution
structure of the wafer structure according to FIG. 4J is shown. In
the wafer structure 100 of the present embodiment of the invention,
the layout path L1 and the layout path L2 are crisscrossed but not
short-circuited, because the redistribution layer 129 and the
second redistribution layer 132 are disposed on different
layers.
[0032] Despite the method of fabricating redistribution structure
disclosed above is exemplified by three layers of the passivation
layers 118, 140, and 170 and two layers of the redistribution
layers, the invention is not limited thereto. The redistribution
structure of the invention can be formed by alternately stacking N
layers of the redistribution layers and (N-1) layers of the
passivation layers, and a metallic pillar is added to the
(N-1).sup.th passivation layer to fill the indented portion of the
redistribution structure, so that the top portion of the metallic
pillar has the same height with the top portion of the (N-1).sup.th
passivation layer. Therefore, various redistribution structures are
disposed at the same horizontal height before the UBM layer is
formed. The UBM layers and the bumps are subsequently formed using
the same material, having the same specifications and following the
same manufacturing process, therefore the bumps have the same
height.
[0033] According to the wafer structure and the method for
fabricating the same disclosed in above embodiment of the
invention, the bumps formed after redistribution have the same
height. In the wafer structure of the invention, a metallic pillar
is added to the redistribution structure to fill the indented
portion formed in the redistribution structure extended from the
original position of the solder pad. Therefore, the UBM layers and
the bumps subsequently formed using the same material, having the
same specifications and following the same manufacturing process
would have the bumps of the same height. Besides, the contact
between the redistribution layer and the metallic pillar as well as
the contact between the metallic pillar and the UBM layer are
excellent, avoiding the problem of detachment.
[0034] While the invention has been described by way of example and
in terms of a preferred embodiment, it is to be understood that the
invention is not limited thereto. On the contrary, it is intended
to cover various modifications and similar arrangements and
procedures, and the scope of the appended claims therefore should
be accorded the broadest interpretation so as to encompass all such
modifications and similar arrangements and procedures.
* * * * *